Gears are representative mechanical elements that efficiently transmit the desired amount of power or rotational motion. Thus, a large number of gears are used in transmission devices, gear shifters, and the like, and in a planetary gear mechanism of a gear shifter, for example, internal gears having arc-shaped teeth are widely used.
The processing accuracy for the gear has a direct effect on vibrations and noise in the device where the gear is used, and such gears have conventionally been ground as a finishing process for the gears. The above-mentioned grinding method for the internal gear having arc-shaped teeth is disclosed in Patent Document 1, for example.